High quality three color photothermographic silver halide (i.e., dry silver) imaging constructions based on diffusion transfer of imaging dyes from imaging layers to a strippable image-receiving layer are known in the art. Those multilayer constructions require barrier interlayers between the imaging layers to prevent penetration of upper layers into the lower layers during solvent coating and drying operations, and to prevent crosstalk during development of the latent image following exposure. However, the barrier interlayers must also allow transfer of imaging dyes (formed during development) by diffusion to the image-receiving layer.
It is also desirable that the polymer coated as the image-receiving layer have high permeability to imaging dyes. In full color dry silver constructions, the various imaging dyes often have widely different chemical structures and, therefore, quite different tendencies to migrate in polymer films.
Dry silver compositions or emulsions are photothermographic compositions, and contain a light-insensitive, reducible silver source; a light-sensitive silver source; and a reducing agent for the light-insensitive, reducible silver source. The light-sensitive material is generally photographic silver halide, which must be in catalytic proximity to the light-insensitive, reducible silver source. Catalytic proximity requires an intimate physical association of these two materials so that when silver specks or nuclei are generated by the irradiation or light exposure of the photographic silver halide, those nuclei are able to catalyze the reduction of the light-insensitive, reducible silver source by the reducing agent. It has been long understood that silver (Ag.degree.) is a catalyst for the reduction of silver ions and the silver-generating light-sensitive silver halide catalyst progenitor may be placed into catalytic proximity with the silver source in a number of different fashions, such as by partial metathesis of the light-insensitive, reducible silver source with a halogen-containing source, coprecipitation of silver halide and light-insensitive, reducible silver source material, and other methods that intimately associate the silver halide and the silver source.
In both photographic and photothermographic emulsions, exposure of the photographic silver halide to light produces small clusters of silver atoms. The image-wise distribution of these clusters is known in the art as a latent image. This latent image generally is not visible by ordinary means, and the light-sensitive article must be further processed to produce a visual image. The visual image is produced by the catalytic reduction of silver ions, which are in catalytic proximity to the silver halide grains bearing the latent image.
Typically, in color dry silver imaging systems a leuco dye is incorporated as a reducing agent for the light-insensitive, reducible silver source, generally in combination with a spectral sensitizer for the silver halide. The leuco dye is oxidized to form a dye upon development, thereby giving a colored image. In full color constructions, spectrally-sensitized emulsion layers containing yellow, magenta, and cyan leuco dyes are typically coated onto a substrate and separated by one or more barrier interlayers.
Residual silver stain is a major problem with dry silver color constructions known in the art. This has been overcome by causing the developed dye image to diffuse from the dry silver layer to an image-receiving layer that is then stripped from the emulsion layer(s). In this case, a barrier interlayer must serve the dual roles of separating the chemistry of neighboring emulsion layers, and allowing diffusion of the dye image under thermal processing conditions.
Depending on the particular ingredients of a given dry silver layer, the development may be best carried out, for example, under acidic or basic conditions.
When multiple dry silver layers with incompatible developing chemistries are employed, it is very difficult to keep development conditions within the dry silver layer from affecting the development of nearby or adjacent dry silver layers. As a result, it is advantageous to coat dry silver layers with different developing conditions on opposite sides of a transparent substrate.
U.S. Pat. No. 4,594,307 discloses a heat developable photographic material that produces a pure and stable dye image by the oxidation-reduction reaction between a reducible organic silver salt and a leuco dye reducing agent wherein the dye image formed is transferred to an image-receiving layer by continuing the heating for development to separate the dye image formed from the silver images and other residual chemicals. However, this material is not capable of producing a multiple color or full color image on the same substrate.
The generation of color dry silver images has been accomplished using microencapsulated constructions and tri-pack (yellow/magenta/cyan) multilayer constructions, such as those disclosed in U.S. Pat. Nos. 4,883,747 and 4,923,792. The cited patents above employed S-97 Gantrez.TM. polystyrene, 523 Vinol.TM. partially hydrolyzed polyvinyl acetate, and B-76 Butvar.TM. polyvinyl butyral as barrier interlayers. These constructions generally have substantial silver and sensitizer stain present that affects the image color separation. The stain problem can be overcome by causing the developed dye image to diffuse from the image-forming layers into a receptor layer that is subsequently stripped from the rest of the construction. The success of this type of approach hinges in large part on the barrier interlayers between the image-forming layers of the tri-pack construction selectively permitting migration of the image-forming dyes while controlling the migration of other image-forming layer components, particularly leuco dyes.
U.S. Pat. No. 4,021,240 shows multiple layers in column 22, lines 7 to 65 and column 23, lines 1 to 57. Interlayers of polyvinyl alcohol are used to preserve the integrity of the color-forming layers. Other hydrophilic polymers, such as gelatin, are also useful. The use of other synthetic polymeric binders alone or in combination as vehicles or binding agents in various layers is also disclosed. Useful resins such as polyvinyl butyral, cellulose acetate butyrate, polymethyl methacrylate, ethyl cellulose, polystyrene, polyvinyl chloride, chlorinated rubber, butadiene-styrene copolymers, and vinyl chloride-vinyl acetate copolymers are also disclosed.
Multicolor photothermographic imaging articles are known in the art with the various color-forming layers separated from each other by functional or nonfunctional barrier layers between the various photosensitive layers. Photothermographic articles having at least two or three distinct color image-forming layers are disclosed in U.S. Pat. Nos. 4,021,240 and 4,460,681.
A process for forming an image in which mobile dyes are released by using the coupling reaction of a reducing agent oxidized by an oxidation-reduction reaction with silver halide or an organic silver salt at high temperature has been described in European Patent No. 79,056, West German Patent No. 3,217,853 and European Patent No. 67,455.
Copending U.S. application Ser. No. 07/775,193 discloses multicolor dry silver imaging constructions that require dye diffusion to an image-receiving layer. No mention is made in that application to the specific polymers employed herein, or to the particular advantages obtained by their use.
Copending U.S. application Ser. Nos. 07/895,045, 07/870,916, and 07/871,005 disclose various dye diffusive dry silver articles employing vinylidene chloride-containing copolymers as interlayer materials for selective dye diffusion.